Production of alkali metal hydrides



Patented Apr. 18, 1950 UNITED STATES PATENT OFFICE 2,504,927 PRODUCTION or ALKALI METAL mamas Virgil L. Hansley, Niagara Falls, N. Y., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware netal hydrides.

process. preparing such metal hydrides and particularly No Drawing. Application April 15, 1947, Serial No. 741,699

13 Claims. (Cl. 23-204) This invention relates to the production of alkali metal hydrides.

involves adding to the mixture of molten metal I and finely divided solid inert material a small amount of a hydrocarbon which has at least 8 carbon atoms and is capable of reacting with the alkali metal to form an alkali metal hydrocarbide to facilitate dispersion of molten metal over the inert solid material and thereby increase the rate of hydrogen absorption. Examples of such hydrocarbons are the isomeric cym'enes, isopropyl benzene, the isomeric isopropyl naphthalenes,

anthracene and the like. Preformed alkali metal a hydrocarbides of such hydrocarbons may also vbe used.

Itis an object of the present invention to provide an improved process for producing alkali A further object is to provide an improvement of the above Freudenberg et al. A still further object is a method for sodium'hydride whereby the rate of reaction is greatly increased with a resulting increase in the space-time yield to obtain alkali metal hydride in a highly reactive, white, finely divided form. Still further objects will be apparent from the ensuing description.

The above objects are accomplished in accordance with the invention by mixing a molten alkali metal with a finely divided solid material and a relatively small amount of a dispersing agent which may be an acetylenic hydrocarbon having the structural group -CECH or an alkali alkali metal may be used.

I have discovered that the presence of a hydrocarbon of the above type, or an alkali metal derivative thereof, in the mixture of molten I alkali metal and finely divided solid inert material facilitates the dispersion of the alkali metal over thesolid material and results in a substantially greater rate of absorption of hydrogen by the reaction to produce the metal hydride. The chemical identity of the agent which actually functions as the dispersing agent is not known. It is known, however, that effective dispersement of the sodium may be accomplished by adding either, for example, acetylene or a sodium derivative thereof, such as sodium acetylide (NaCzH) or sodium carbide (NaaCz). When either acetylene or sodium acetylide is used, it is probably rapidly converted to sodium carbide. It is not known however, whether the latter functions as the active dispersing agent or is decomposed or adds acetylene under the conditions of use to form the actual active agent. Insofar as the present process is Iconcerned, substantially the same results are achieved whether acetylene, sodium acetylide or sodium carbide, or one of the other above mentioned acetylenic hydrocarbons, is added as suggested. Accordingly, in describing and claiming the invention all such compounds are referred to as dispersing agents since they either act per se as the dispersing agent or form the active dispersing agent under the conditions of use.

In carrying out the process, the molten alkali metal and solid inert material may be mixed together with, for example, acetylene, after which the mixture may be subjected to the action of hydrogen. Alternatively, sodium acetylide or sodium carbide may be added to the mixture of metal and solid material prior to or simultaneously with the introduction of hydrogen. A particularly convenient mode of operation involves the addition of hydrogen containing a small amount of acetyl cue to an agitated mixture of the molten metal and inert solid material. If desired, the acetylene may be added separately from the hydrogen,

metal derivative of such a hydrocarbon, and rew either continuously or i tly. acting the mixture with hydrogen at a temperaonly a relatively Small amount of the p ture above the melting point of the alkali metal. s agent need be p n in h m xture of mol- As typical of t acetylenic hydrogen-bong t t ten metal and solid material to effect excellent ;ma,y be employed I ti acetylene, methyl 45 dispersion of the molten metal over the solid maacetylene, ethyl acetylene, n-propyl acetylene, terial. Generally, amounts of from 0.05 to about isopropyl acetylene, vinyl acetylene and phenyl 1% based upon the combined weight of the alkali acetylene. In place of such hydrocarbons, alkali "metal and inert Solid material is S fi t to metal derivatives thereof in which the hydrogen ive excellent r l r r mounts, '6. a, up in the CECH group has been replaced by an 50 to 10%, maybe used but are not recommended.

Sodium hydride prepared by the method of my Patent 2,372,671 tends to be somewhat discolored due apparently to the formation of free carbon resulting from pyrolysis of the dispersing agent employed. Thus, when using p-cymene or other aromatic hydrocarbon, products having a grayish color are usually formed. In contrast, products prepared in accordance with the present invention using, for example, acetylene as the dispersing agent are white in color. Furthermore, they are much more finely divided than prior products, their particle sizeranging from about 1 to 10 m'icrons,:as compared with products obtained by my previous method whose particle size generally is 100 microns or greater. The present product is much more reactive for use in catalyzing various organic reactions, e.-g., condensations of the Claisen type, and the presence therein of small quantities of the dispersing agent has no deleterious efiect.

The invention is further illustrated by the following examples:

Example 1 .A small cylindrical steelreaction vessel was .fitted with a gas inlet and outlet and a convenranged to rotate horizontally about its axis at about '100 R. P. M. A few small pieces of iron were placed-in the vessel to assist in stirring the charge. A constant temperature air bath was arranged around the vessel in order to aid maintaining the desiredreaction temperature.

Sufficient preformedfsodium hydride to occupy 10-15 .oft'hevolumewas charged into the vessel whilecold, the vessel having previously been filled with nitrogen. The charge was heated to 300- 385% C.'whi le rotating thevessel'and while passing-ina slowstream of hydrogen. An increment of molten sodium was added to the sodium hydride and the'passage of hydrogen was continued at such a rate that only a few bubbles escaped per minute while continuing rotation of the vessel and while'maintaining the temperature within the vesse'lat the "level indicated. The hydrogen emiployed contained "a small amount of acetylene. When the first increment of sodium had been re- :acted, another increment was added without intermediate :cooling and :the cycle repeated. The resultstabulated .below show the production of sodium. hydride going through 10 such cycles or runs. As thezreaction vessel filled due to the production of sodium hydride, .some of the product .wasdischarged, but sufiicient was left in the vessel to constitute a. heel 'for the next run. In adding sodium tcthe hydride heel it is not advisable to .add more than about 20% by weight of sodium based. upon the weight of the heel.

'In 'thefollowing table, the weights of hydride heel at the-beginning of several runs are shown .along with. the rates at which hydrogen was ab- 'sorbed'. In the runs indicated, the amount of acetylene employed varied between about 0.05 and 0.5% based upon the combined weight of the heel and'the sodium.

C2132, Wt. Per Cent H2 absorption,

H el, g.

Example 2 This example consists of three cycles or runs carried out as described in Example 1. In place of acetylene, however, p-cymene was employed as the dispersing agent in amounts which varied between 1 to 3% of the weight of the charge.

The rate of hydrogen absorption was substantially greater in Example 1 than in Example 2, even though p-cymene was employed in the latter casein concentrations much g e te t an was acetylene. Furthermore, the product obtained in Example '2 had 'a grayish color, whereas the product of Example 1 was almost pure white. "Also, the product (if-Example 1 was visibly more finely divided and substantially more reactive than the productcfflilxample 2.

My process is suitable for making the hydride or any of the'alkali metalai. 'e. sodium, potassium, lithium, cesium and rubidium. Mixtures of one or more of the alkali metals'may be reacted with hydrogen according to the present process to produce mixtures of alkali-met'al hydrides.

The hydrogenation reaction-may be carried out in accordance with'theihvention at a temperature "just'a'bove the melting point cf'the alkali metal although the rate-'ofreacti'on at such temperature is-"low. Temperatures as high as 500 to 600 'C. may bejused provided suflicient hydrogen pressure is employed to prevent undue decomposition oi the hydride product. The preferred temperature range is'2 00 to 450 "C.

The process will generallybe carried out at or slightly above atmospheric pressure although pressures substantially above or below atmospheric pressure may be employ'e'd if desired. As indicated above, when relatively high temperatures areirseii pressures above atmospheric will generally be required. Other gases may be introduced with the 'liydr'ogenand such gases may be-inert 'diluents or may bereactive gases to produce a'mixture of the hydride and another alkali metal compound. For ordinary purposes however, such other'ga'ses 'will'not be used and except perhaps for the presence of a small amount of acetylene or other acetylen'ic hydrocarbon substantially pure hydrogen-will generally be employed. I

The finely divided inert solid material emp'loyed'in starting the process as a carrier for the molten alkali metal may be any material such as "sand, clay, various powdered metals and the line, including salts which arefinfusilivle and inactive towards the reactants "present under the conditions of use. r'pr'efer',howevergto use preformed alkali metal hydride and particularly preformed al'kali'imetalhydride or'the metal which is to be hydrogenated- Thus,- m for-m-ing sodium hydride, sodium hydride ts used "as" carrier "for the molten sodium.

.IJclaim .1. A method for preparing "an alkali metal hydride comprising reacting hydrogen "with a mixture-of a relatively small" amount of an alkali metal andaa relatively large amount of .a finely divided solid material in the presence of a'modicum: ofa reaction. product or an alkali metaland an acetylenic compound, said reaction product having an alkali metal atom directly attached to at least one of two carbon atoms which are directly joined to each other by a triple bond, at a temperature above the melting point of the alkali metal.

2. The method of claim 1, wherein the reaction product of an alkali metal and an acetylenic compound is present in an amount equal to 0.01 to 1% based upon the combined weight of the alkali metal and the solid material.

3. The method of claim 1 wherein the acetylenic compound is acetylene.

4. The method of claim 1 wherein the alkali metal is sodium.

5. The method of claim 4 wherein the temperature is between the melting point of sodium and 600 C.

6. The method of claim 4 wherein the reaction temperature is 200 to 450 C.

7. A method of producing an alkali metal hydride comprising agitating a mixture of an alkali metal and at least 80% by weight of a finely divided inert solid carrier therefor at a temperature between the melting point of said metal and 600 C. in the presence of hydrogen and supplying to said mixture a modicum of an acetylenic hydrocarbon.

8. The method of claim 7 wherein the acetylenic hydrocarbon contains less than 5 carbon atoms.

9. The method of claim 8 wherein the acetylenic hydrocarbon is acetylene and is supplied in an amount equal to 0.05 to 0.5% based on the weight of said mixture.

10. The method of claim 9 wherein the solid carrier is an alkali metal hydride.

11. The method of claim 10, wherein the alkali metal is sodium and the solid carrier is sodium hydride.

12. The method of claim 11 wherein the temperature is 240 to 450 C.

13. A method of producing sodium hydride comprising agitating a mixture of sodium and at least by weight of sodium hydride at a temperature of 240 to 450 C. while supplying to said mixture hydrogen containing 0.05 to 0.5% of acetylene based upon the weight of said mixture.

VIRGIL L. HANSLE'Y.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,958,012 Muckenfuss May 8, 1934 2,372,670 Hansley Apr. 3, 1945 2,372,671 Hansley Apr. 3, 1945 

1. A METHOD FOR PREPARING AN ALKALI METAL HYDRIDE COMPRISING REACTING HYDROGEN WITH A MIXTURE OF A RELATIVELY SMALL AMOUNT OF AN ALKALI METAL AND A RELATIVELY LARGE AMOUNT OF A FINELY DIVIDED SOLID MATERIAL IN THE PRESENCE OF A MODICUM OF A REACTION PRODUCT OF AN ALKALI METAL AND AN ACETYLENIC COMPOUND, SAID REACTION PRODUCT HAVING AN ALKALI METAL ATOM DIRECTLY ATTACHED TO AT LEAST ONE OF TWO CARBON ATOMS WHICH ARE DIRECTLY JOINED TO EACH OTHER BY A TRIPLE BOND, AT A TEMPERATURE ABOVE THE MELTING POINT OF THE ALKALI METAL. 